The invention relates to chromatographic treatment of pectin-containing vegetable material, such as sugar beet pulp. The invention relates particularly to separating pectin and pectic sugars/oligomers and simultaneously salts from pectin-containing vegetable material by using chromatographic fractionation.
Pectin is a commonly used additive in food industry. It is useful, for example, as a stabilizing agent, thickener and gelling agent in, for example, jams and other fruit-based products as well as in sour milk-based products, such as yoghurts.
For the separation of pectin, the vegetable material used as a starting material, such as sugar beet pulp, is first brought into a soluble form by using, for example, acidic or basic hydrolysis. During the hydrolysis, salts are introduced into the solution which are usually undesired in the final pectin product and which should thus be removed.
Pectins have conventionally been produced from apples, sugar beet pulp or the citrus peel by first extracting soluble polymers with acid, whereafter the obtained solution is filtered and concentrated and the pectins are precipitated with alcohol or metal salts at a suitable pH. Free sugars remain in the alcohol-water solution. Since the amounts of solvent utilized in the method are large, the sugar content in the alcohol-water solution is extremely low.
U.S. Pat. No. 4,816,078 (Sxc3xcddeutsche Zucker-Aktiengesellschaft) describes the recovery of L-arabinose from sugar beet pulp or other vegetable material by basic hydrolysis, the L-arabinose being subsequently chromatographically purified. U.S. Pat. No. 5,250,306 (British Sugar PLC) discloses the recovery of araban from sugar beet pulp by first using basic hydrolysis and then ultrafiltration. In the basic hydrolysis according to this publication, pectin is destroyed and only sugars can be recovered.
WO 99/10542 (Cultor Corporation) describes the recovery of L-arabinose from sugar beet pulp using chromatographic separation with a cation exchanger in a monovalent metal form. This process includes, as a preceding step, extraction of sugar beet pulp with a strong alkaline solution. The use of strong alkali destroys pectin compounds, whereby only sugars are recovered.
JP Patent 56 011 903 (Chisso Corporation) describes the use of ultrafiltration for separating xe2x80x9ccrudexe2x80x9d pectin from vegetable material. The starting material is first treated with hydrochloric acid at a pH 2.5 to 3.0, and pectin is extracted at a temperature of 85xc2x0 C. The obtained product is purified by filtration, and the filtrate is ultrafiltrated by using a membrane having a cutoff size of 6000 to 20 000 Da.
U.S. Pat. No. 5,008,254 (Weibel, M. K.) discloses a method wherein fast acidic hydrolysis is conducted at a high temperature (120xc2x0 C.) for a short period of time (six seconds) in order to recover a pectin-sugar mixture from sugar beet pulp. The hydrolyzed mixture containing sugars and some pectin compounds is concentrated by ultrafiltration (cut-off size 30 000 Da). Said fast acidic hydrolysis is extremely complex technically, and the insoluble fibres which remain when the acidic hydrolysis is used tend to disintegrate into colloidal mass which is difficult to filter.
DE Patent Specification 4 313 549 (Herbstreich and Fox KG Pektin FA) describes a method of preparing a pectin-containing extract from sugar beet material. In the method, the raw material is hydrolyzed with a citric acid solution at a temperature varying between 50xc2x0 C. and the boiling temperature of the solution.
U.S. Pat. No. 5,660,872 (Raffinerie Tirlemontoise S. A.) describes a method of chromatographic fractionation of a polydispersed saccharide composition. The method relates particularly to separating inulin fractions. The inulin-containing material to be treated may be obtained from, for example, vegetable material such as chicory root. The raw material is first brought into a soluble form and subsequently into the form of a metastable solution by adjusting the temperature of the solution below the solubility temperature without the solution being agglomerated. The solution in the metastable form is chromatographically fractionated into a fraction of high molecular weight free from saccharides of low molecular weight (polymerization degree 2 or less, preferably 5 or less), and a fraction of low molecular weight free from saccharides of high molecular weight (polymerization degree higher than 5). The method is unable to separate salts from saccharide components.
Chem. Abstr., vol 123 (1995), ref. 137780 describes the recovery of pectic polysaccharides from vegetable material, such as apple and and citrus fruit, using anion-exchange columns. The reference does speak anything about the simultaneous recovery of salts and sugars. Chem. Abstr. vol. 55 (1961), ref. 22994i describes chromatographic fractionation of polysaccharides, such as a mixture of sugar beet araban and citrus pectin, using sellulose anion exchangers. In the alkaline conditions used in connection with the anion exchangers, pectin is easily destroyed.
Chem. Abstr., vol. 67 (1967), ref. 12777e relates to the use of ion exchangers in the production of beet pectin. In this process, metal salts are removed from sugar beet pulp hydrolysate.
SE-B 453511 (Nils Monten) describes the preparation of a pectin product from sugar beet pulp using an anion exchanger. The anion exhanger is used for purification purposes, not for separating pectin from oligomeric and monomeric sugars. The product is thus a mixture of pectin polysaccharides and oligomeric and monomeric sugars.
WO 99/19365 (Korea Institute of Science and Technology) relates to the preparation of a therapeutic composition including galacturonic acid (pectin), arabinose and galactose. In this process, pectin and other desired components are precipitated with ethanol from an aqueos extract of Angelica gigas Nakai followed by treating the pectin precipitate with an anion exchange resin. This process requires the use of an organic solvent (ethanol).
In connection with the present invention, pectins refer to polysaccharide compounds of high molecular weight being composed of partly methylated polygalacturonic acid chains (polygalacturonic acid content at least 65%). Pectin also contains araban, galactan and xylose side chains attached to the polygalacturonic acid chain, and rhamnoses interrupting the continuous polygalacturonic acid chain. Furthermore, the galacturonic acid groups of sugar beet pectin are partly acetylated.
In connection with the present invention, the expression xe2x80x9cpectin-containing vegetable materialxe2x80x9d refers to any pectin-containing material obtained from plants. The pectin-containing vegetable material is typically obtained from sugar beet, citrus fruit or apples.
In connection with the present invention, pectic sugars/oligomers refer to polysaccharides, oligosaccharides and mono- and disaccharides, such as arabans of low molecular weight, arabino-oligomers, arabinose, galactans, galactose, galacto-oligomers, rhamnose and fucose, which are present together with pectin in the pectin-containing vegetable material. The mixture to be treated may also contain small amounts of sucrose, glucose and fructose.
In connection with the present invention, sugar beet pulp refers to pulp which is obtained in connection with the production of sugar and which remains after sugar extraction and from which the sugars have to a large extent been extracted.
In connection with the present invention, a sugar beet pulp hydrolysate refers to hydrolyzed sugar beet pulp which contains pectins and special sugars as well as salts to be separated and which is in the form of a solution.
In connection with the present invention, salts refer to small-molecular ionized substances, typically to inorganic small-molecular ionized substances such as sodium salts, potassium salts and calcium salts. Typically, the salts are the sodium, potassium and/or calcium salts of inorganic acids, such as hydrochloric acid, sulphuric acid and/or nitric acid. These are typically in salt form in a neutralized solution and in ion form in an acidic solution. The salts mainly originate from the pretreatment, such as acidic or basic hydrolysis and potential neutralization, of pectin-containing vegetable material, such as sugar beet pulp.
The method of the invention has been successfully used for separating pectins and pectic sugars/oligomers into separate products while salts have simultaneously been removed from the pectins and pectic sugars/oligomers. The method in its entirety is conducted in an aqueous solution. This enables inflammability and toxicity problems relating to the use of organic solvents, such as isopropanol and ethanol, to be avoided.
Since the separation method of the invention is, in addition to size exclusion, also based on ion exclusion and/or ion retardation, the ion contents of different fractions can be controlled at the same time. In addition to separating ions, a resin regenerated to an ion form acts as a cation exchanger, removing cations (e.g. crome, iron) contained in the feed solution by exchanging them for the ions of the regenerated resin. The cut-off limits for the collection of fractions in the chromatographic separation can be determined so as to control the composition of different fractions.
Objects of the invention are achieved by a method which is characterized by what is set forth in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.